Auto Doctor: Car clunking can be normal

Dear Doctor: I have a 2010 Mercury Mountaineer with 28,000 miles. When I am at highway speeds and take my foot off the gas, there is a "clunk" noise that sounds similar to the universal joint failure in the old rear wheel drive cars. The problem is most notable at highway speeds, but can be heard at lower speeds during deceleration as well as acceleration. -- Sam

Dear Sam: Your Mountaineer has an all-wheel-drive system so any wear or worn universal or C/V joints will cause a clunk sound. Even some extra free play in the front or rear differentials will cause a clunk sound on and off the gas pedal. A small amount of noise is considered normal. -- Junior Damato, Motor Matters

Dear Doctor: I have replaced motor mounts about every 23,000 miles on my Mazda3. It now has 94,000 miles. Is there a defect in the car? -- Jan

Dear Jan: I also replace engine mounts and have tried the aftermarket engine mounts; these do not last long, especially on vehicles with manual transmissions. I would check all engine mounts for movement. If you replace one or two mounts and the others have movement, then the replacement mounts will fail early. -- Junior Damato, Motor Matters

Dear Doctor: Last summer I bought a black 2013 Honda Accord V-6. After the second week I found a chip on the hood. Now this winter I have found six chips on the hood. It's kept in the garage and only driven when roads are dry and clean. Have you heard of Honda having "soft paint" issues? -- Bob

Dear Bob: Hood chips are common, as are small chips in windshields. The hood slope invites small rock damage with the low profile design. You are not alone with this problem of chipping paint on hood surfaces. I would as the dealer to set up a meeting with the Honda zone representative to look at the hood. There is touch-up paint you can get from Honda and dab the spots. It does not take much to cause a chip in the hood or windshield. -- Junior Damato, Motor Matters

Dear Doctor: I recently purchased a 2014 Mercedes Benz C300 sedan. Occasionally, when the engine is fully warmed up the transmission shifts roughly at low speeds -- usually when downshifting after pressing the accelerator or braking. It seems to jerk/buck in the lower gears almost like being lightly rear ended. It shifts fine at higher speeds. Any idea what might be going on? -- Eric

Dear Eric: Check with the dealer about any updates that available. The transmission is electronically controlled. The reason it seems to act up when the engine is warm is because in a cold engine state all engine and transmission functions are controlled from pre-set computer settings in closed loop. -- Junior Damato, Motor Matters

Dear Doctor: I have a 2008 Chrysler Sebring convertible. The battery has been replaced three times. The dealer has performed diagnostic testing, but found no drain. Why are the batteries going bad? -- Gloria

Dear Gloria: You did not mention how long or often you drive the car. Fuel-injected vehicles have multiple computers that require constant battery voltage, even when the vehicle is parked and locked. The vehicle will need to be checked for current (parasitic) drain. The maximum parasitic drain is 50 mili amps on this car. At the maximum drain it will take six to eight weeks to run the battery down. You should invest in a small battery maintainer. There are many battery options on every vehicle, especially the battery cold cranking rating also known as reserve power. I always suggest a battery replacement with the largest cold cranking power available. The new AGM advanced technology has much more available power and is worth the extra cost. -- Junior Damato, Motor Matters

Dear Doctor: I have a 2002 Mazda Millenia with 75,000 miles. The "check engine" show codes p0750, p0755, p0760 and p071743. It also has a bad connection with clip on top of transmission. Can you help? -- Roy

Dear Roy: You will need to see a technician who will connect a professional scan tool and check it under the vehicle specific mode. This takes time and will result in a complete accurate code test. Road testing the vehicle with the scan tool connected is also recommended. It could be a poor ground connection or faulty solenoid. -- Junior Damato, Motor Matters